Typical miniature DC electric motors have a metallic cylindrical motor housing formed of mild steel or the like and defining a hollow tubular section and an integral bottom. One end of the motor housing is open to receive a motor cover, which encloses the open end of the motor housing. The motor cover includes a brush arm holder that may comprise a separate brush base, or the brush base may be an integral part of the motor cover. Within the motor housing are fixed a pair of opposite permanent magnets, each of which has an arc shape to match the inner wall of the housing. The magnets form between them a volume in the housing for a rotor. The rotor typically includes a cylindrical armature coaxially mounted on a rotor shaft. The rotor shaft extends through the opposite ends of the motor housing. Bearings may be used to rotatably support the rotor shaft in the ends of the housing. For example, the bottom of the motor housing may have an integral flange, into which a bearing can be press-fitted to support one end of the rotor shaft. The end cap may have a similar bearing structure. In this way, the rotor shaft is held in coaxial alignment with the motor housing.
The brush holder supports a pair of brush arms which provide an electrical connection to an external electrical contact of the motor. The brush arms are generally strips of copper having a first end which serves as the external electrical contact and an opposite, free end on which is mounted a brush. The brush arms are fixed to the periphery of the brush holder and are attached to opposite sides of the brush holder. The brushes located on the brush arms face each other at the axis of the motor. When inserted in the housing, the brushes are in slidable contact with a commutator on the rotor shaft. The commutator provides an electrical contact between the wiring of the armature and the brushes. The armature may include any suitable number of wire windings, such as three windings. The external contacts of the brush arms provide DC current through the brush arms to the brushes. The brushes provide DC current to the commutator. The commutator provides DC current to the windings in the armature. Electrical current input through the armature creates an alternating magnetic field within the housing that interacts with the magnetic field of the permanent magnets. This interaction of magnetic fields creates a force that rotates the rotor. This rotation drives the rotor shaft to provide a mechanical rotational output power source from the rotor. The rotor shaft extends through the bottom of the housing to provide a mechanical power output to drive a gear box or other device. Exemplary miniature electric motors and particular components thereof are shown in, for example, U.S. Pat. Nos. 6,528,922; 6,717,322; 5,294,852; 5,010,264, the disclosures of which are incorporated by reference herein.
Such miniature electric motors can be and are used in a variety of applications, including, but not limited to, motorized toys, audio and video equipment, hand tools and other electrical motor-driven devices, vehicles or appliances. Miniature DC electric motors tend to be a relatively-low cost component of toys and other equipment. Accordingly, it will be appreciated that it is desirable to reduce the manufacturing costs and complexity associated with making such motors. It is also desirable for various applications incorporating miniature electric motors in a variety of exemplary scenarios to reduce unwanted electromagnetic noises in the electrical input supplied to the motors, as one skilled in the art will appreciate from the description herein.
Shown in FIG. 1 is an example of a conventional DC electric motor brush base and brush arms assembly 100 for attachment to motor cover 128 at brush base attachment section 126 thereof. Assembly 100 includes a first elongated metal strip forming brush arm 106, having a brush 114 on one end and external electrical contact 118 (including soldering hole 110) on the other end, and a second elongated metal strip forming brush arm 108, having brush 116 on one end and external electrical contact 120 (including soldering hole 112) on the other end. Brush arms 106 and 108 may comprise of any electrically conductive metal, but are typically fashioned from copper.
In a conventional assembly method, brush arms 106 and 108 are inserted into opposite ends of brush base 104 at brush arm elbow sections 122 and 124 to form brush base and brush arms assembly 100. FIG. 2 is a sectional view of assembly 100 which shows brush arms 106 and 108 inserted into opposite ends of brush base 104 at brush arm elbow sections 122 and 124. FIG. 3 is a side view of assembly 100 showing longitudinal line bifurcating the assembly along the length of brush arm 106. FIG. 4 shows a cross section of assembly 100. As shown in FIG. 1, assembly 100 is inserted into motor cover 128 at brush base attachment section 126, thereby fixing brush arms 106 and 108 to the inside area of motor cover 128.
FIG. 1 also shows a conventional through-hole type capacitor 102 having two electrically conductive metal wire legs 102a and 102b extending downward and outwardly from the body of the capacitor. In a conventional motor assembly using a capacitor in the electric input circuit for filtering electromagnetic noises, wire legs 102a and 102b of capacitor 102 are electrically connected to brush arms 106 and 108 at external electrical connections 118 and 120 by threading wire legs 102a and 102b through holes 110 and 112, respectively, and soldering the wire legs to the external electrical contacts at holes 110 and 112 and then cutting off any residual metal wire to ensure fitment. FIG. 5 shows a conventional DC electric motor 130 including motor cover 128 attached to motor housing 132 and rotor shaft 129 extending through opposite ends of motor 130. FIG. 5 also shows capacitor 102 soldered to external electrical contacts 118 and 120 at solder holes 110 and 112 in accordance with the conventional assembly method. As shown in FIG. 5, under the conventional assembly method capacitor 102 is located outside the motor cover and motor housing.
This conventional design and assembly method entails a number of problems including, for example: (i) difficulty inserting the wire legs of the capacitor through small holes in the external electrical contacts of the brush arms before the capacitor can be soldered into place; (ii) difficulty soldering the wire legs to the external electrical contacts of the brush arms; and/or (iii) difficulty controlling the consistency of the quality of the soldered connection. Also, the conventional design and assembly method locates the capacitor outside of the protective motor cover and motor housing, where the capacitor is more susceptible to physical damage during assembly, installation and/or use.
FIG. 6 shows a prior art motor cover 200 for use in a miniature, DC electric motor by Johnson Electric. The Johnson design shown in FIG. 6 uses a chip capacitor 202 and choke coil 204 located in the motor cover to form an “L-C” circuit to suppress the electrical noise generated from the commutation between the two brushes and the commutator. As shown in FIG. 6, the chip capacitor in Johnson's design is located on one side of the motor cover opposite to the side where brush arms 206 and 208 are located.
Thus, it will be appreciated that there is a need in the art for a motor assembly design, and/or method of making the same, that overcomes some or all of these and/or other problems and/or that effectively provides for DC electric motor input noise filtering using a simplified and cost efficient manufacturing approach.
One aspect of certain exemplary embodiments relates to a simplified electric motor design, and/or a method of making the same.
Another aspect of certain exemplary embodiments relates to a capacitor in an electric motor input circuit for filtering electromagnetic noises.
Still another aspect of certain exemplary embodiments relates to a capacitor supported or held between two brushes of a motor assembly and in a solderless electrical connection therewith.
In certain exemplary embodiments, a motor assembly for an electric motor includes an electric motor having a motor cover, a brush base for holding two brush arms, and a chip capacitor having two terminal ends with the first terminal end in solderless surface contact with the first brush arm and the second terminal end in surface contact with the second brush arm.
In certain exemplary embodiments, a motor assembly for an electric motor includes a brush holder, a chip capacitor, and two brush arms, with at least one of said brush arms shaped to support or hold the capacitor between the two brush arms and in surface contact therewith.
In certain exemplary embodiments, a method for assembling a DC electric motor including inserting two brush arms into a brush base at opposite sides of a hollow space provided in the brush base and inserting a ceramic chip capacitor in the hollow space between the two brush arms such that one terminal end of the capacitor is in surface contact with one of the brush arms and the other terminal end of the capacitor is in surface contact with the other brush arm.
These features, aspects, and advantages may be combined in any suitable combination to realize yet further exemplary embodiments.